1. Field of the Invention
The present invention relates to image observation apparatus and systems and is preferably applicable to image observation apparatus and systems, for example, constructed in such structure that a scene of the outside world (an outside image or outside information) captured by an image pickup optical system (image pickup system) is displayed on a display device (image display means) to permit an observer to observe it, or to image observation apparatus and systems designed for the purpose of permitting the observer to have various pseudo experiences while displaying an image (virtual image) artificially produced by a computer or the like or an image recorded by a video system or the like over the real scene (outside information) on the image display means.
2. Related Background Art
There are conventionally known image observation devices constructed in such structure that the outside image (outside information) is converted to an electric signal by an image pickup device such as a CCD camera or the like, it is displayed on a display device (display means) such as a CRT, an LCD or the like, and the observer is allowed to observe the outside image through an eyepiece optical system (such observation will hereinafter be referred to as “video seethrough observation”) as if he or she were observing the outside by the naked eye.
There are also the image observation devices proposed in such structure that the outside image picked up by the camera is displayed in combination with the image created by computer graphics or the like or with an image recorded by the video system or the like so as to permit the observer to observe a synthetic scene of the real space and the virtual space.
In the image observation devices of these structures, in order to match positions of objects etc. in the observing direction with those in the observation by the naked eye, the outside optical axis of the image pickup optical system of the image pickup system is aligned with the eye-side optical axis of the eyepiece optical system of the display system and the entrance pupil of the image pickup optical system is located at the position equivalent to the entrance pupil of the ocular optical system.
It is, however, expeimentally verified that, when the image pickup optical system is located at the exactly equivalent position against the ocular optical system, there arises the problem that an object displayed on the image display means is perceived in the size smaller than that in the observation of the outside by the naked eye.
FIG. 28 provides the results of experiments for comparison between perceived sizes in the observation by the naked eye and in the video seethrough observation with a device wherein the image pickup optical system is located at the optically, exactly equivalent position relative to the ocular optical system, where an object of a certain size was observed at different distances. FIG. 28 shows a graph of the perceived size of the object plotted against the distance to the object.
In FIG. 28, the solid line represents the results in the observation by the naked eye and the dashed line the results in the video seethrough observation. It is understood that the object in the video seethrough observation is significantly perceived in the size smaller than that in the observation by the naked eye.
FIG. 23 is a schematic diagram to show the main part of a conventional image observation system wherein a pair of image observation devices each having the image pickup system and the display system are provided for the left and right eyes of the observer. In the drawing, elements for the left eye are accompanied by suffix L and elements for the right eye by suffix R. It is noted that the suffixes L, R indicating the elements for the left and right eyes are omitted in the description below.
In FIG. 23, each image pickup system 100 is composed of an image pickup optical system 101 and an image pickup device 102, and numeral 103 designates the outside optical axis of the image pickup optical system. A mirror 104 separates optical paths of display system 110 from those of the image pickup system 100. Each display system 110 is composed of a display optical system 111 and a display element 112, and numeral 113 designates the eye-side optical axis of the display optical system.
A pair of such image observation devices each consisting of the image pickup system 100 and the display system 110 are provided for the left and right eyes. E represents the observing eyes.
The image pickup systems 100 and the display systems 110 illustrated in FIG. 23 are constructed in such structure that the center 102C of the image pickup device 102 and the optical axis 103 of the image pickup optical system 101 are matched with the center 112C of the display element 112 and the optical axis 113 of the display optical system and that the optical axes 103R, 103L of the image pickup optical systems for the left and right eyes and the optical axes 113R, 113L of the display optical systems are inclined at the angle θ so as to intersect at a reference position 120 located in the outside.
A plane 112′ (virtual image screen) in conjugate with the display element 112 with respect to each display optical system 111 is matched with a plane 102′ (focal plane) in conjugate with the image pickup device 102 with respect to the image pickup optical system 101, and center positions 102C′, 112C′ of the respective planes are matched at the reference position 120. The center positions for the left and right eyes are also matched at the reference position 120.
FIG. 24 and FIG. 25 show a situation in which with the image observation system illustrated in FIG. 23, the object 130 in the outside space is imaged by the image pickup systems 100 to be displayed by the display systems 110 and in which the observer is observing the object image.
In FIG. 24, the object 130 in the outside space is in focus on the image pickup devices 102 via the mirrors 104 and the image pickup optical systems 101 to form images 131 thereon to be picked up. The position of each image corresponds to a spot 131′ on the focal plane 102′ conjugate with the image pickup device 102, and is a distance P apart from the center 120 of the focal plane.
The image 131 of the object 130 taken by the associated pickup system 100 is displayed as an image 132 on each display element 112 as illustrated in FIG. 25. In FIG. 25, light from each display element 112 is guided to the observing eye E by the mirror 104 and the display optical system 111. Each observing eye E observes the corresponding image 132 as an image 132′ on the virtual image screen 112′ conjugate with the display element 112. The position of each image 132′ is a distance Q apart from the center 120 of the virtual image screen.
The observer observes the image 132′R by the right eye ER and the image 132′L by the left eye EL. This permits the observer to observe the object 130 as if it were actually present at an intersection 134 between the visual axis 133R of the right eye ER and the visual axis 133L of the left eye EL. At this time, where the entrance pupil position of each image pickup optical system 101 is matched with the entrance pupil position of the corresponding observing eye E and where the angle of image pickup view and the angle of display view are equated, the position and size of the focal plane 102′ of each image pickup system are matched with those of the virtual image screen 112′ of the associated display system, so that the distance P becomes equal to the distance Q. Therefore, the position of the intersection 134 becomes the same as the actual position of the object 130 in the outside space and the reproduced object size also becomes equal to that of the object 130.
In the image observation system illustrated in FIG. 23, if the image pickup optical systems 101 have the zooming function or if the display magnification is varied by use of an electronic zoom or the like, there will occur cases in which the reproduced space is distorted or cases in which the observer fails to effect the fusion of the images for the left and right eyes.
This phenomenon will be described below with reference to FIG. 26, FIG. 27A, and FIG. 27B. FIG. 26 shows a case of observation where the picked up images of the object 130 in the outside space as illustrated in FIG. 24, acquired by the image pickup systems 100, are displayed at the magnification of 2 on the display elements to be observed. The distances S from the screen center 120, of the display images 135′ on the virtual image screens 112′ are twice the distances Q in FIG. 25. Just as in the case of FIG. 25, the observer can observe the object 130 as if it were actually present at the intersection 137 between the visual axis 136R of the right eye ER and the visual axis 136L of the left eye EL. The observer can observe the object as if he or she became closer to the object or as if the object became larger.
However, the visual axes of the left and right eyes can intersect with each other (or the left and right images can undergo fusion) only if the object 130 is within the XZ plane (Y=0). FIG. 27A is a YZ section in the state illustrated in FIG. 25 and FIG. 27B a YZ section in the state illustrated in FIG. 26. In FIG. 27A and FIG. 27B, suffixes y, z attached to Q and S indicate a Y-directional component and a Z-directional component thereof, respectively.
As illustrated in FIG. 27A, where the images are picked up by the image pickup systems without use of the zooming function to be displayed by the display systems and be observed, the visual axes 133R, 133L of the left and right eyes ER, EL agree in the YZ plane and thus intersect with each other even if the object 130 is not present in the XZ plane (Qy ≠0). However, where the zooming function is used as illustrated in FIG. 27B, the visual axes 136R, 136L of the left and right eyes ER, EL do not agree in the YZ plane and thus do not intersect with each other. Deviation is permitted to some extent if it is small, but it will induce fatigue of the observer and distortion of the reproduced space. With large deviation, there will arise the problem of failure in the fusion of the left and right images.
Not only in the cases using the zooming function, but also in the cases wherein the angle of image pickup view does not agree with the angle of display view because of design factors, production errors, etc., the above-stated problem will arise.